1. Field of the Invention
This invention relates to a spectral image-obtaining apparatus for obtaining object images with desired wavelengths in observation apparatuses, for example, such as endoscopes, microscopes, and surveillance cameras and relates to a method for obtaining spectral image.
2. Description of the Related Art
In recent years, a method in which spectral images are acquired with specific wavelengths in accordance with uses in observation and the acquired spectral images are displayed on a display device to be observed has been used for observations with observation apparatus such as endoscopes.
For example, so-called “special light observation” has been widely used for the sake of early detection of minute legion such as cancer or for the sake of detailed diagnosis of lesion area before surgery, and, in the special light observation, the particular structures of tissues are highlighted and are displayed by performing light wavelength control that is different from that for normal light observation.
Methods of special light observation includes: narrowband imaging (NBI) in which capillaries in the superficial layer of mucous membrane are highlighted and displayed by acquiring images formed by narrow band light of about 400 nm that is easily absorbed by hemoglobin in blood, or vessels in the middle layer of a tissue are highlighted and displayed by acquiring images formed by narrow band light of about 550 nm that is easily absorbed by hemoglobin; and near-infrared fluorescence observation in which deep vessels are observed by acquiring images formed by near-infrared fluorescence of about 850 nm that occurs in irradiation of near-infrared excitation light of about 800 nm to fluorescent substances such as indocyanine green (ICG) which are intravenously injected, for example.
For example, an etalon-type spectral element disclosed in Japanese Patent TOKUKAI No. 2002-148528 is publically known as a conventional optical element for obtaining spectral image. The etalon-type spectral element is a variable spectral transmittance element in which a reflexive film is provided on each of a pair of substrates made of light-transmitting material. And, the etalon-type spectral element can transmit light of a particular wavelength according to a distance between the substrates each having the reflexive film.